JPH0355521B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) In recent years, as copying machines have become faster, there has been a trend for carrier iron powder used in copying machines to be not only spherical and have a fine particle size, but also lightweight and with a smooth particle surface. The present invention relates to a method for producing spheroidized reduced iron powder, particularly spheroidized reduced iron powder suitable for use as a carrier iron powder for dry copying. (Prior art) In an attempt to obtain spheroidized reduced iron powder,
In Publication No. 19667 or Special Publication No. 53-3011,
Techniques have been disclosed for spheroidizing irregularly shaped raw material iron powder by oxidizing and burning it, and then reducing it at a predetermined temperature. By the way, although the spheroidization of the iron powder is maintained in the reduced iron powder obtained in this way, the oxide film is actually removed during the reduction process, and the surface has unevenness like spongy iron. Since the powder was melted once, it was dense and heavy, with many coarse particles. For this reason, when such iron powder is used for the carrier of a copying machine, it has a problem in that it does not stand up well, making it impossible to obtain clear images, especially in high-speed copying machines. Regarding this point, the inventors previously proposed
In Publication No. 169129, we proposed hollow spherical iron oxide powder and its production. However, this invention is aimed at obtaining an iron oxide-based carrier iron powder, and is not intended for pure iron-based spheroidized reduced iron powder required depending on the type of copying machine, but for carrier iron powder for high-speed copying machines. At present, the technology for obtaining spheroidized reduced iron powder suitable for powder has not yet been developed. (Problems to be Solved by the Invention) The purpose of the present invention is to solve the problems that have occurred in conventional spheroidized reduced iron powder, and to provide an advantageous manufacturing method for obtaining spheroidized reduced iron powder that is light and has a smooth surface. This is where we propose. (Means for Solving the Problem) This invention reduces and sinters iron oxide powder of iron ore powder or mill scale powder, and reduces the amount of residual oxygen obtained.
Spongy iron powder of 0.3 to 2.0 wt% is pulverized to 10 mm or less, and then the pulverized particles are guided into a turbulent flow of high wind speed to cause the pulverized particles to repeatedly collide with each other to be pulverized. This is a method for producing spheroidized reduced iron powder, which is characterized by producing spherical powder in which 80% or more of the particles have a particle size of 74 μm or less, excluding the initial stage of pulverization. This invention was developed as a result of various experimental studies to obtain a reduced iron powder with a sharp particle size distribution of 74 μm to 44 μm, which is particularly suitable for carrier iron powder for dry copying, and which is lightweight and has a smooth surface. This is based on new knowledge that it is extremely effective to make iron powder porous to obtain powder, and that it is extremely effective to repeatedly grind using a turbulent flow method with high wind speed, rather than mechanical grinding. be. (Function) In this invention, first, residual oxygen is 0.3 to 2.0wt.
It is necessary to obtain % spongy iron powder. The reason for this is that if the residual oxygen content is less than 0.3%, it becomes difficult to crush the particles due to collisions between particles. On the other hand, if it exceeds 2.0wt%, in the subsequent process,
When performing deoxidation treatment, the heat treatment time will be longer,
As a result, the particles become pseudo-particles. Therefore, it is necessary to reduce and sinter the raw material to obtain spongy iron powder containing 0.3 to 2.0 wt% of residual oxygen. Next, the reason for pulverizing the obtained spongy iron powder to 10 mm or less is that if the size exceeds 10 mm, it is difficult to crush the pulverized particles by repeatedly colliding with each other in pulverization using a turbulent flow method with high wind speed. This is because. This invention produces reduced iron powder that is lightweight and has a smooth surface by introducing the spongy iron powder into a pulverizer that generates turbulent flow at high wind speed and repeatedly crushing the particles by collision with each other. can be easily obtained. In addition, when reducing and firing the raw material iron powder, the raw material iron powder is charged into a cylindrical chemical-resistant container together with carbon material for reduction, and the raw material iron powder is reduced and fired in a tunnel furnace consisting of preheating, firing, and cooling zones. , a method of reducing in a reducing atmosphere of hydrogen gas using a fluidized bed reduction furnace, a method of reducing with carbon material using a rotary kiln, a shaft furnace, etc. can be adopted as appropriate. (Example) FIG. 1 shows an example of a process for producing spheroidized reduced iron powder suitable for the present invention, and the diagram will first be explained. In the figure, 1 is a hopper for sponge iron, 2 is a feeder for cutting out a fixed amount of sponge iron from hopper 1, and 3
is a bucket conveyor, 4 is a collection hopper,
5 is a pulverizer using a turbulent flow method with high wind speed for turning the spongy iron powder supplied from the collecting hopper 4 into fine spherical powder, and 6 is a damper. Also,
Reference numeral 7 denotes a blower for guiding the iron powder crushed by the crusher 5 to the cyclone, where the air sucked by the blower 7 goes directly to the dust collector, and a part of it is circulated to the crusher 5. 8 is a cyclone, 9 is a cyclone rotary valve, 10 is a loading screen, 11 is a screen, 12 is a switching damper, and 13 is a product hopper. The manufacturing process shown in Figure 1 is designed to make iron powder spheroidal and not generate ultrafine powder. In this example, in order to obtain spheroidized iron powder with a sharp particle size distribution of mainly 74 to 44 μm, mill scale powder was first used as a raw material, charged into a refractory container together with carbon material, and then heated in a tunnel furnace. 1150 at
A sponge iron with residual oxygen of 0.9% was produced by reduction firing at 45H at ℃. Next, the obtained sponge iron was pulverized to 5 mm or less with an impeller breaker (not shown), and the pulverized particles were supplied to a sponge iron hopper 1 and processed according to the process shown in FIG. A 74 μm screen is installed in the screen 11 to obtain iron powder of −74 μm or less, and the iron powder collected on the Rhodes screen 10 is again supplied to the crusher 5 to ensure that 80% or more of the iron powder is 74 μm or less. Grinding and sieving were repeated so that the following results were obtained. Here, most of the iron powder of 74 μm or less that is sieved at the initial stage of crushing by repeated collisions is easily broken into fine particles, and the surface has not yet become smooth spheroidized iron powder. It is necessary to take out the product from the product hopper 13. In order to remove such iron powder, it is desirable to remove it when the number of times the iron powder remaining on the screen is re-pulverized, that is, the number of times the crushed particles are repeatedly collided with each other, is as high as possible, but if the number of times is too high. If the amount increases, it is disadvantageous in terms of yield, so we recommend using a type of grinding that reduces the amount of iron powder as much as possible without deteriorating the yield, for example, iron powder that becomes 74 μm after 6 to 8 grinding times. It is better to remove it. Note that the opening of the screen 11 is set to 74 μm because normally the screen 11 has a smaller opening so as to obtain fine iron powder, but the efficiency of the screen decreases due to tearing or clogging. Furthermore, if the sieved fine iron powder returns to the crusher 5, there is a risk of ignition, so a screen with an opening of 74 μm is suitable for industrial production. Figures 2a and 2b are electron micrographs (×200, ×400) of the obtained iron powder A. As is clear from FIGS. 2a and 2b, many spheroidized iron powders are seen and the surface thereof is smooth. Figures 3a and b show the results obtained by pulverizing according to the process shown in Figure 1 and sieving using a screen with an opening of 105 μm.The number of repeated collisions is 6 to 8. Electron micrograph of iron powder B that does not intend to become spheroidized (×
200, ×400). Iron powder A shown in Figure 2 a and b is an example of a case obtained by repeating crushing and sieving (approximately 40 times) until the iron powder of 74 μm or less becomes 80% or more (approximately 40 times). Iron powder with a particle size of 74 μm or less that has been produced up to 8 times is removed from the product hopper), and spheroidized reduced iron powder is produced by inducing frequent collisions between particles using a turbulent flow method with high wind speed. It was confirmed that it was obtained. Next, in order to use the obtained iron powder as an iron powder raw material for copying machines, it was annealed in ammonia decomposition gas so that the oxygen content was 0.5% or less and the carbon content was 0.05% or less. The treatment conditions were a temperature of 900°C and a duration of 1 hour. After annealing, the cake-like iron powder was crushed and sieved to remove pseudo particles, and the quality and particle size distribution of the iron powder are shown in Table 1 for iron powders A and B, respectively. In this example, the test amount per test was 10 tons, and Table 1 shows the average value X and standard deviation value σ for n=20 (number of times). As is clear from Table 1, in this implementation, 80% or more of the iron powder was 74 μm or less, and it was found that the spheroidized reduced iron powder had an extremely sharp particle size distribution.

【table】

[Table] When this iron powder was stabilized using iron powder A shown in Table 1 and applied to a high-speed copying machine as an iron powder for the carrier of a copying machine, clear images could be obtained. . (Effects of the Invention) According to the present invention, it was possible to easily obtain a light and smooth-surfaced spheroidized reduced iron powder suitable for carrier iron powder for copying machines, especially high-speed copying machines.

[Brief explanation of drawings]

Figure 1 is a diagram showing a manufacturing process suitable for this invention, Figures 2a and b are photographs of the particle structure of spheroidized reduced iron powder, and Figures 3a and b are photographs of the particle structure of reduced iron powder of a comparative example. be.

Claims (1)

[Claims] 1 Residual oxygen amount 0.3 to 2.0wt obtained by reducing and firing iron oxide powder of iron ore powder or mill scale powder
% spongy iron powder is pulverized to 10 mm or less, and then the pulverized particles are introduced into a turbulent flow of high wind speed so that the pulverized particles repeatedly collide with each other to be pulverized, and the initial stage of pulverization due to the repeated collisions Particle size 74μm excluding
A method for producing spheroidized reduced iron powder, characterized by producing spherical powder containing 80% or more of the following: